The most effective antiperspirant active for an aerosol formulation on the market today is activated aluminum chlorohydrate (AACH). The AACH powder has Al:Cl atomic ratio of greater than 1.90 and mostly about 2.0, and has Band III polymer concentration of at least 20% and Band IV polymer concentration of less than 10%, when analyzed by the size exclusion chromatogram (SEC) using a high performance liquid chromatograph (HPLC).
Antiperspirant stick formulations can use the more efficacious materials, such as activated aluminum zirconium salts. However, aerosol spray formulations cannot use the activated aluminum zirconium salts due to the safety concern of inhalation of zirconium compounds. Therefore, aerosol spray formulations use the active containing Al salts only.
U.S. Pat. No. 4,359,456 to Gosling et al. discloses an improved Al active material through the process of heating from 2.5% to 8.5% by weight of aluminum concentration to have Band III polymer concentration of at least 20%. It discloses that the presence of Al polymers of above 100 Angstroms is not necessary to provide the high efficacy. The improved Al active material, disclosed in Gosling et al., i.e. basic aluminum chloride, has Al:Cl atomic ratio from about 0.5 to about 3.3. However, the salts having the Al:Cl ratio above 2.1 are not considered to have any antiperspirant properties, and therefore are not classified as conventional antiperspirant actives. Moreover, at lower Al:Cl ratio of about 0.5, it would be almost impossible to have at least 20% of Band III polymers.
U.S. Pat. No. 4,944,933 to Inward discloses a process of making a basic aluminum chloride in a powder form having Al:Cl atomic ratio of from 1.7 to 2.2 and having Band III polymer concentration of at least 20%. The process involves dissolving Al metal powder in aluminum chloride to form the final basic aluminum chloride solution of 7.5% to 13% by weight with reaction time being within 5 hours at 50° C.-105° C. and drying the BAC solution to powder. Even though the active salt prepared according to the process has high Band III polymer concentration, the Al polymer species, however are mostly Al13 species characterized by 27Al NMR having chemical shift at 62.5 ppm that provide low antiperspirant efficacy.
U.S. Pat. No. 5,718,876 to Parek et al. discloses basic aluminum halides and nitrates having enhanced antiperspirant efficacy that are produced by reacting aluminum metal with aluminum halide or nitrate solution at temperature greater than 85° C. with Al/anion ratio of about 1.2-1.8. The active solution has 30-40% of anhydrous weight having less than 20% of Band III polymers. Parek et al. discloses the concentrated Al sesquichlorohydrate solution with low amount of Band III polymers.
U.S. Pat. No. 8,883,129 to Swaile et al. discloses a method of making an active having enhanced antiperspirant efficacy comprising an Al-only salt having a Band III polymer concentration of at least 20% and no more than 20% of Al monomer. The method includes (a) making an aqueous solution of an aluminum salt having at least 20% of Band III polymers, (b) adding an aqueous solution of a monomeric aluminum salt to solution (a), and (c) rapidly drying the mixture to form a product. By minimizing the contact time between (a) and (b), Swalie et al. will maintain the monomeric state and acidity of the monomeric aluminum salt. The contact time varies from 1 second to 30 minutes depending on the temperature. Long contact time allows the monomeric aluminum salt to be neutralized by the aluminum hydroxychloride to form aluminum dimers, trimers and polymers. However, addition of very acidic aluminum chloride to diluted and activated aluminum solution will produce free acid upon spray drying that will not only corrode the spray dryer, but also cause the formation of colored specks, such as in black, brown, yellow and green colors. It will also generate the hygroscopic powder that is difficult to formulate. Specifically, if the active salt of Swaile et al. is formulated into an aerosol, the acidic and hygroscopic powder can corrode the orifice nozzle of the aerosol spray can, and also form larger agglomerates, clogging the orifice and preventing the spray from coming out of the aerosol can.
US patent application 2006/0104918 to Brown et al. discloses a suspension aerosol composition comprising milled AACH and a masking oil having reduced levels of white deposits. However, the very fine particles generated by milling process may pose health hazard for inhalation when used in an aerosol formulation.
Therefore, there is a need for a new and improved Al active material with enhanced antiperspirant efficacy for aerosol application, which is not too acidic and not too highly hygroscopic and/or does not pose safety concerns of inhalation of hazardous material.